1. Field of the Invention
The present invention relates to a degraded performance recovery method for a lithium ion secondary battery. The present application claims priority to Japanese Patent Application No. 2015-154077 filed on Aug. 4, 2015, the entire contents of which are hereby incorporated by reference.
2. Description of the Related Art
Since lithium ion secondary batteries are less in weight and higher in energy density than the presently available batteries, they have been used in recent years as the so-called portable power sources for personal computers, portable terminals, and the like, and as drive power sources for vehicles. In particular, the lithium ion secondary batteries are expected to be hereinafter increasingly popular as high-output drive power sources for vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV).
However, lithium ion secondary batteries use various rare metals and are relatively expensive. For example, active materials thereof use such rare metal as cobalt (Co). For this reason, from the standpoint of efficiently using natural resources and reducing the running cost, the need for restoring lithium ion secondary batteries which have degraded over a long period of use and extending the service life (ensuring the long life) thereof has been growing year by year.
As a cause of degradation of lithium ion secondary batteries, a process is known in which components in an electrolytic solution are decomposed during charging and discharging, a coating film including, for example, phosphorus atoms as the decomposition product is formed on the electrode surface, and the battery performance is degraded as a result thereof. To resolve this problem, Japanese Patent Application Publication No. 2012-022969 discloses a reuse method by which a spent lithium ion secondary battery is disassembled, the electrodes thereof are washed with a polar solvent to remove the compounds causing the degradation, the electrodes are thereafter dried, and the battery is reassembled.